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Weekend project design.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Weekend project design.

Unread postAuthor: El Chupacabras » Fri Feb 01, 2013 9:52 pm

Hi everybody, this is my first post here, so have as much mercy as possible please.
Ok as a curious person, I found a post on the web "Piston Valves Explained Visually", and I used the animations to finally understand the whole concept of pilot-chamber-piston relationship. Together with an instructable from Mr Crowley, I came up with a design that is supposed to work as a fully auto gun (I hope anyway) that i've discussed with Mr Crowley and he thinks it might not work as fully auto. He suggested that I put it here, so here it is for your consideration.
According to my understanding, as the pressure in the chamber and in the pilot reaches the relief valve's top pressure, it should open and the bullet get fired.

Any comments, suggestions, etc are of course welcome.
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Unread postAuthor: Gippeto » Sat Feb 02, 2013 1:57 am

You DO know we have a member who goes by Goatz? :lol:
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Unread postAuthor: yodabeast14 » Sat Feb 02, 2013 11:08 pm

Your probably gonna want to put some type of sliding piece of metal where your magazine and your barrel meet so that your air dosnt just dump into the magazine
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Unread postAuthor: jackssmirkingrevenge » Sun Feb 03, 2013 1:11 am

The design should work in theory, but your main tank is going to need to be quite large/high pressure for a significant number of shots.

Gippeto wrote:You DO know we have a member who goes by Goatz? :lol:


HAHAHAHHAHA! :D :D :D

*ahem*

Your probably gonna want to put some type of sliding piece of metal where you're magazine and you're barrel meet so that you're air dosnt just dump into the magazine


Not necessary, worked fine for me here: http://www.spudfiles.com/forums/i-has-f ... 17845.html
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Unread postAuthor: El Chupacabras » Sun Feb 03, 2013 1:25 pm

Well, finally someboby wrote something related to the design lol.
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Unread postAuthor: El Chupacabras » Sun Feb 03, 2013 1:28 pm

Let's see..
According to my calculations the tank should hold close to 500 psi, hopefully more, as it was designed to withstand more than 1 ton of hidraulic pressure.
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Unread postAuthor: sagthegreat » Sun Feb 03, 2013 2:53 pm

*COUGH COUGH* Titianium Tubing
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Unread postAuthor: El Chupacabras » Sun Feb 03, 2013 3:35 pm

Hahahaha..

Naaah not titanium, but it should withstand a lot of pressure. It's a shock absorber and they do take the weight of a car and maybe more when the car hits a pothole without busting.
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Unread postAuthor: Gippeto » Sun Feb 03, 2013 8:27 pm

El Chupacabras wrote:Let's see..
According to my calculations the tank should hold close to 500 psi, hopefully more, as it was designed to withstand more than 1 ton of hidraulic pressure.


Hope you're not confusing lbs force with hoop stress.

You know about Barlows formula?

How do you intend to join the assembly? Pinned with bolts in shear or threads in shear?
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Unread postAuthor: El Chupacabras » Sun Feb 03, 2013 8:59 pm

Um.. I plan to put a quick release valve for the tank. the rest is going to be welded.
I just checked Barlow's law, and these are the results:

According to Barlow's law, P equals 1440, but just in case, re check for me please. These are the figures:

T = 0.12"
D = 1.5"
S = 9000 psi.
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Unread postAuthor: jackssmirkingrevenge » Mon Feb 04, 2013 1:00 am

El Chupacabras wrote:Um.. I plan to put a quick release valve for the tank. the rest is going to be welded.


You mean a quick connect coupling right?

Image

This type of setup needs a lot of tuning, so make sure your pressure relief valve is adjustable. Also, what do you plan on using as a trigger? Are you going to make your own balanced valve, or use an existing valve like a blowgun?
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Unread postAuthor: El Chupacabras » Mon Feb 04, 2013 8:03 am

Yes is a quick connect valve that looks very much like the one on the bottom right.

The relief valve is fully adjustable, starting at 30 psi up to 100 psi if I'm not mistaken.

As a trigger, if you take a close look at it, I designed a piston that slides inside a small brass tee (inside the tank) that goes connected to the quick connector's male and sticks out of the tank in order to be connected to the female (on the outside body of the pilot). Once the trigger is pulled, the small piston will let air out towards the pilot, and... you know the rest.
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Unread postAuthor: Gippeto » Mon Feb 04, 2013 10:32 am

El Chupacabras wrote:According to Barlow's law, P equals 1440, but just in case, re check for me please. These are the figures:

T = 0.12"
D = 1.5"
S = 9000 psi.


While I don't have any doubts about 1.5"x.120" wall seamless steel tubing handling 500psi pressure, I do have a couple questions for you.

Curious as to where you got a material strength of 9000psi. Is this for papier mache? :)

Also need to know what you used as a safety factor. Would suggest nothing less than 3.

Welded = non serviceable...this may...and likely will...come back to bite you.
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Unread postAuthor: El Chupacabras » Mon Feb 04, 2013 1:15 pm

Um... Let's see... I used a safety factor of 4. Math and I aren't very good friends though, but you say 120(?) I don't know if you made a typing mistake. What I'm using as a tank is the hidraulic part of a shock absorber. I cut the top part, took out the piston and all the valves, together with an inner piston that comes inside. I then measured the thickness of the wall that gave me the measurement of 1 mm (I don't have the tool for measuring in inches), but converted it to inches and the aproximate value is that of a cold rolled sheet metal piece Cal. 0.12 which is quite thick.
Now you say welding is not recommended, but there is no other way to seal the top of the tank but welding a thick washer with the inside small enough for the quick coupling to stick out and be welded to the washer.
The welding is going to be done in a factory that makes tanks so it is very likely to be very well done, as they have special welding equipment.
Now you're starting to worry me :shock:
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Unread postAuthor: Gippeto » Mon Feb 04, 2013 2:26 pm

Now you're starting to worry me


Right back at ya.

1mm = 0.039"

What KIND of tanks does this factory make?
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